1. Field of the Invention
The present invention relates to structured packing for multi-phase process towers including both vapor-liquid and liquid-liquid process towers and, more particularly, to a packing made up of corrugated, louvered contact plates disposed in face-to-face contact for use in such process towers.
2. History of the Prior Art
In the vapor-liquid and liquid-liquid contact art, it is highly desirable to utilize methods and apparatus that efficiently improve the quantity of the mass and/or heat transfer occurring in process towers. The technology of such process towers is replete with various packing designs used for tower packing. The types of packing employed are functions of the particular process to be effected within the tower. The packing elements may thus comprise a structured array (structured packing) arranged to form a regular array inside the column or relatively small shapes such as rings or saddles dumped into and randomly arranged (dump packing) within the tower. Close fractionation and/or separation of the feed stock constituents introduced into the tower and the elimination of harmful or undesirable residual elements impart criticality to the particular vapor-liquid or liquid-liquid contact apparatus chosen for a given application. The shape of the dump or structured packing elements determines the flow patterns in and density of the array and the resultant resistance to flow caused thereby. Prior art structured packing arrays have thus found utility in a variety of shapes, sizes, and material forms.
It has been found particularly desirable in the vapor-liquid contact portion of the prior art to provide apparatus and methods affording efficient heat transfer, fluid vaporization, or vapor condensing duty whereby cooling of one of the fluids can be accomplished with a minimum pressure drop through a given zone of minimum dimensions. High efficiency, low pressure drop, and reduced temperature gradients are important design criteria in the chemical engineering art, such as petroleum fractionation operations. Vapor-liquid process towers for effecting such operations are generally of the character providing descending liquid flow from an upper portion of the tower and ascending vapor flow from a lower portion of the tower. Sufficient surface area for vapor-liquid contact is necessary for the primary function and the reduction or elimination of liquid entrainment present in the ascending vapor. Most often it is necessary for the structured packing array to have sufficient surface area in both its horizontal and vertical planes so that fractions of the heavy constituents are conducted downwardly in condensed form and the vapors are permitted to rise through the packing with minimum resistance. With such apparatus, heavy or light constituents of the feed are recovered at the bottom and top of the tower, respectively, by the interaction of the ascending vapor and descending liquid, mostly upon the surface of the structured packing. Similar considerations apply to the design of towers for liquid-liquid extraction operations.
Similarly, it has also been found desirable in the liquid-liquid contact portion of the prior art to provide apparatus and methods affording efficient heat transfer, or liquid-liquid contact whereby contact of the fluids can be accomplished with a minimum pressure drop through a given zone of minimum dimensions. High efficiency and low pressure drop are important design criteria in liquid-liquid extraction operations. Mass transfer liquid-liquid process towers for effecting such operations are generally of the character providing descending heavy liquid flow from an upper portion of the tower and ascending light liquid from a lower portion of the tower. Sufficient surface area for liquid-liquid contact is necessary for the primary function and the reduction or elimination of heavy liquid entrainment present in the ascending lighter liquid. Most often it is necessary for the structured packing array to have sufficient surface area in both its horizontal and vertical planes so that fractions of the heavy constituents are conducted downwardly and the lighter liquid is permitted to rise through the packing with minimum resistance. With such apparatus, heavy or light constituents of the feed are recovered at the bottom or top of the tower, respectively, by the interaction of the ascending light liquid and descending heavy liquid, mostly upon the surface of the structured packing.
In a vapor-liquid tower a plurality of stacked layers affording compatible and complemental design configurations are generally assembled within a single process column. When used in vapor-liquid applications, each layer utilizes the velocity and kinetic energy of the ascending vapors to perform the dual function of eliminating liquid entrainment in the ascending vapor and the thorough and turbulent contacting of the vapor with the descending liquid to accomplish sufficient separation or fractionation of the fluids into desired components. Quick cooling of the ascending vapor is generally a prerequisite for efficient operation to effect efficient heat transfer for vapor condensation and minimum pressure drop in a minimum vertical depth of the packing. Oppositely inclined, corrugated lamellae, or plates, have thus been utilized in the prior art for affording multiple vapor passages through the horizontal and vertical planes of the packing layers to insure the flow of vapor and distribution thereof within the lamellae and to prevent maldistribution, or channeling, of the vapor through certain portions of the layers and not others. Only in this manner is efficient and effective utilization of the column and the energy applied therein effected.
In a liquid-liquid tower a plurality of stacked layers affording compatible and complemental design configurations are generally assembled within a single process column. Each layer utilizes the velocity and kinetic energy of the fluids to perform the dual function of eliminating heavy liquid entrainment in the ascending liquid phase and the thorough contacting of the light and heavy liquids to accomplish sufficient separation or extraction of the fluids into desired components. Oppositely inclined, corrugated lamellae, or plates, have thus been utilized in the prior art for affording multiple light phase passages through the horizontal and vertical planes of the packing layers to insure the flow of lighter liquid and distribution thereof within the lamellae and to prevent maldistribution, or channeling, of the lighter liquid through certain portions of the layers and not others. Only in this manner is efficient and effective utilization of the column and the energy applied therein effected.
In vapor-liquid applications the structural configuration of inclined, corrugated contact plates of the prior art variety often incorporates holes for vapor passage. Vapor turbulence is created by such holes to insure intimate vapor-liquid contact. It is also necessary to insure that the ascending vapor performs a dual function of liquid contact and liquid disentrainment within close proximity to the vertical location at which the ascending vapor approaches or leaves the vapor passage holes. In this manner maldistribution of the ascending vapor or descending liquid is reduced.
In liquid-liquid applications the structural configuration of inclined, corrugated contact plates of the prior art variety often incorporates holes for liquid passage. Turbulence is created by such holes to insure intimate light and heavy phase contact. It is also necessary to insure that the ascending light phase performs a dual function of phase contact and liquid disentrainment within close proximity to the vertical location at which the ascending phase approaches or leaves the passage holes. In this manner maldistribution of the ascending or descending phases is reduced. It is, moreover, a paramount concern of the prior art to provide such methods and apparatus for vapor-liquid or liquid-liquid contact in a configuration of economical manufacture. Such considerations are necessary for cost-effective operation.
Oppositely inclined corrugated plates provide but one method and apparatus for countercurrent, liquid-vapor, or liquid-liquid interaction. With such packing arrays, the liquid introduced at or near the top of the column and withdrawn at the bottom is effectively engaged by vapor or a second liquid stream being introduced at or near the bottom of the column and withdrawn at the top. The critical feature in such methods and apparatus is to insure that the liquid and vapor (or second liquid) achieve the desired degree of contact with each other so that the planned mass or energy transfer occurs at the designed rate. The internal structure is, of course, passive in the sense that it is not power driven externally and has few, if any, moving parts.
The prior art is replete with passive vapor-liquid and liquid-liquid contact devices utilizing cross-fluted and perforated sheets of material in face-to-face engagement. This configuration encourages the liquid moving through the packing to form itself into films having, in the aggregate, a large area over which the light phase may pass. However, the design problem is not merely a matter of providing a large surface area or a multitude of corrugations, cross-flutes, or perforations. A number of other interrelated design considerations must be taken into account, some of which have been mentioned above.
From a process standpoint, it is important that the desired vapor-liquid or liquid-liquid contact interaction be carried as close to completion as possible. For example, in a crude oil vacuum tower, efficient fractionation and good separation are needed to produce oil streams that are free of undesirable residual elements. As mentioned above, the contact column and its internal apparatus must efficiently utilize the heat supplied to the unit. In this manner, direct operating costs are minimized whether the objective is mass transfer, heat transfer, liquid-vaporization, or vapor condensing duty. With the above, pressure drop is a primary consideration as is the vapor-liquid fluid interface. Structured packing for vapor-liquid contact has been shown in the prior art in such references as U.S. Pat. Nos. 3,343,821, issued Sep. 26, 1967; 4,139,584, issued Feb. 13, 1979; 4,128,684, issued Dec. 5, 1978; 3,785,620, issued Jan. 15, 1974; and 3,959,419, issued May 25, 1976.
As pointed out above, the desired vapor-liquid or liquid-liquid contact interaction should be carried as close to completion as possible. For example, in a light hydrocarbons amine contactor, efficient extraction of H.sub.2 S (hydrogen sulfide) is needed to produce fuel streams that are free of undesirable H.sub.2 S pollutant.
In the above-referenced vapor-liquid contact method and apparatus patents, several design configurations are presented for affording intimate vapor-liquid contact. In particular, stacked, corrugated contact plates in face-to-face contact, having corrugations inclined to the horizontal and/or orthogonal one to the other, have been shown and provided in various material configurations. These configurations include monofilament yarns and solid plates. It is, moreover, prominent in the prior art to utilize fluted plates having a plurality of perforations therethrough. One such example is seen in U.S. Pat. No. 4,296,050 issued Oct. 20, 1981, while another is seen in British patent no. 1,004,046, published Sep. 8, 1965.
While many prior art methods and apparatus for vapor-liquid or liquid-liquid contact have been shown to be relatively effective, certain disadvantages still remain. In particular, vapor-liquid contact towers incorporating descending liquid flow and ascending vapor flow of the structured packing variety defined above are generally incapable of readily accommodating internal pressure differentials. Problems also exist with surfaces that face downward because such surfaces are generally not effectively wetted. Even with slits or lancing of the packing there are many downward facing surfaces, and few prior art designs effectively address proper wetting or vapor passage therethrough. This is true even with a plurality of apertures disposed in corrugated and/or cross-fluted plates in face-to-face contact such as those referenced above. Vapor flow is ultimately sensitive to pressure differentials, and is easily diverted between the myriad of exposed areas of mating corrugations or flutes. In phase contact towers incorporating descending heavy liquid flow and ascending light liquid flow of the structured packing variety defined above, difficulties have been encountered in readily accommodating internal pressure differentials. Problems also exist with surfaces that face downward because such surfaces are generally not effectively covered by the liquids. Even with slits or lancing of the packing there are many downward facing surfaces, and few prior art designs effectively address proper coverage of the surface by the heavy phase or light phase passage therethrough. This is true even with a plurality of apertures disposed in corrugated and/or cross-fluted plates in face-to-face contact such as those described above. Light phase flow is sensitive to pressure differentials, and is easily diverted between the many exposed areas of the packing.
It is desirable, in countercurrent flow, that both the liquid and the vapor effectively commingle along uniformly wetted packing surfaces. In order for this to occur, it has been shown to be very beneficial for both the liquid and the vapor to be able to pass through the corrugated sheet for effective interaction. Without the free passage of both vapor and liquid through the sandwiched corrugated sheets, zones of either high or low volume flow can occur. These flow volume differentials result in a lack of uniformity and homogeneity within the packing. The most efficient structured packing configuration incorporates a region wherein the ratios of vapor and liquid remain relatively constant with consistent interaction and mixing. This requires a packing surface facilitating uniform flow of both liquid and vapor through both sides of the corrugated sheets, yet in a configuration promoting uniform wetting and spreading of liquid and equalization of pressure between said sheets. Similar considerations apply in liquid-liquid extraction applications. Thus, in countercurrent flow in liquid-liquid systems, both phases should effectively commingle along uniformly covered packing surfaces. In order for this to occur, it is very beneficial for both the light and heavy phases to be able to pass through the corrugated sheet for effective interaction. Without the free passage of both phases through the sandwiched corrugated sheets, zones of either high or low volume flow can occur. These flow volume differentials result in a lack of uniformity and homogeneity within the packing. The most efficient structured packing configuration incorporates a region wherein the ratios of light and heavy phases remain relatively constant with consistent interaction and mixing. This is best achieved with a packing surface that promotes uniform flow of both phases through both sides of the corrugated sheets, while also promoting uniform spreading of the liquids and equalization of the pressure between said sheets.
It would be an advantage, therefore, to overcome the problems of the prior art by utilizing the flow directing and gathering features of louvers constructed in the corrugated plates. The methods and apparatus of the present invention provide such an improvement over the prior art packing by providing a corrugated plate having a select louver configuration therein. In this manner, liquid is caused to flow upon and through both sides of the corrugations of facing plates in paths which substantially increase the vapor-liquid or liquid-liquid contact of ascending vapor (or liquid) and descending liquid normally passing between said corrugated plates. The presence of selectively oriented arrays of louvers in the corrugated sheets permits vapor (or light liquid) and liquid flows to be exposed on opposite sides thereof while flowing in opposed directions thereacross. Such liquid-vapor (or liquid-liquid) flow configurations maximize mass transfer efficiency and may be provided with a minimal increase in production costs over that of conventional opposed plate corrugation assemblies.